Buying a Spider Monkey is illegal in most countries. It is not possible to purchase a Spider Monkey through any reputable breeder, even in countries where they are legal.
It is also advised against buying one through the exotic pet trade due to potential health and safety issues. The only way that a person may be able to acquire a Spider Monkey is to rescue one or take part in an animal adoption project. Therefore, it is not possible to buy a Spider Monkey legally.
The best way to acquire one is by participating in an animal adoption program.